1. Field of the Invention
The invention relates to a cutting machine for automatic trimming of edges of folded printed products such as brochures, magazines, catalogs, comprising at least one cutting station comprising a knife for the front cut at the open side of the printed products, further comprising a feeding device for the transport of the printed products to the cutting station, and further comprising a transport device for transporting the printed products within the cutting station.
2. Description of the Related Art
Cutting machines of this kind are known in the prior art, for example, from European patent application 0 941 817 of the assignee of the instant application for patent. With such a cutting machine, printed products can be automatically cut or trimmed at the front, at the foot and the head and can thus be trimmed on three sides. In the first cutting station, the front cut and in the second cutting station at the same time the head cut and the foot cut are performed. The printed products are guided within the transport device against mechanical stops with the fold area leading and are aligned at the stops. The fold thus provides a reference edge, and the front cut is performed at a certain spacing to this reference edge. The transport of the printed products into the first cutting station and between the first and the second cutting stations is carried out with upper and lower belts. These belts are intermittently driven by a mechanical step-by-step gear mechanism or by a slider crank.
In order to enable alignment of the printed products at the mechanical stops, they must be released in front of the stops by lifting the upper belts, respectively.
With the known cutting machine, printed products with very different formats and different thickness can be cut. For most printed products, a very precise front cut can be performed with high output, i.e., the spacing between the folded area and the front cut is within the desired tolerances. For thick and bulky printed products these tolerances in the direction of width are relatively great and can be within the range of approximately 1 mm. It was found that such thick and bulky printed products, when reaching the first cutting station, can fan out and this reduces the cutting precision of the front cut. Moreover, it was found that other external effects as well as the occurring acceleration and deceleration values as well as the mechanical play within the gear mechanism can also reduce the cutting precision.
It is an object of the present invention to provide a cutting machine of the aforementioned kind with which smaller cutting tolerances can be ensured even for thick and bulky printed products.
In accordance with the present invention, this is achieved in that measuring means are provided with which, in the cutting station and before reaching the cutting position, the position of each printed product is measured and in that the transport device is controlled based on the result of the measurement such that a deviation from the nominal position is corrected during further transport.
With the cutting machine according to the invention, positional errors of the printed products, which result from fanning out of the printed products during transport as well as from other effects, are corrected based on the position measurement and the corresponding control of the transport device. By means of the control it is possible to correct positional deviations for each individual printed product and to minimize accordingly the cutting tolerances for the product width. When it is determined by position measurement that the printed product is pushed back, it is accordingly accelerated and, in the other case, i.e., when it is advanced too far, it is decelerated.
An important advantage of the cutting machine according to the invention is seen in that the mechanical stops, which are used in the prior art, are now replaced by virtual stops. With the aforementioned control, the printed products can move into a corrected and precise position on the way to a virtual stop. The printed products must no longer be released and can be secured by the upper and/or belts even during the cutting process. Since the printed products must no longer be released and can be accelerated for the further transport without having to lower the upper belts, higher production speeds are possible.
With the machine according to the invention the printed products can also be cut at the front side while running through the machine, i.e., without being stopped, as, for example, in the case of a HT 18 Trimmer by AM Graphics or a device according to European patent application 0 698 451.
The cutting machine according to the invention thus makes possible smaller cutting tolerances and, at the same time, a higher production speed.
A further advantage resides in that the rotational speed fluctuations resulting from the forces of gravity of the cutting apparatus can be smoothed by control of the transport device which results in a more quiet and exact advancing action of the transport device.
According to a further embodiment of the invention, the measuring means have at least one laser photocell. Such a laser photocell makes possible a very precise measurement of the position of the printed products in the first cutting station.
According to a further embodiment of the invention, the transport device is driven by an electronically controlled single drive. The play and wear of conventional mechanical step-by-step gear mechanisms is thus avoided. The movement curves for the electronic step-by-step gear mechanism can be stored as a coordinate table. By doing so, for different production conditions such as, for example, product thickness, paper quality, format, and production speed, special optimized movement profiles can be programmed. For an extreme product change, it is possible by simply switching to a different curve table to program an optimal movement course. Such curve tables can be calculated in a simple way according to known movement laws for cam gears. It is particularly advantageous that in the case of an extreme product change a simple switching to another curve table enables programming of a more optimal movement course.